Oscillators – Electrical noise or random wave generator
Reexamination Certificate
2000-02-16
2003-02-18
Kinkead, Arnold (Department: 2817)
Oscillators
Electrical noise or random wave generator
C331S046000, C331S047000, C708S250000, C708S251000
Reexamination Certificate
active
06522210
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the generation of randomized pulses, and in particular to a random pulse generator having at least three oscillators, wherein the outputs of at least two of the oscillators are combined to disturb the output of a final oscillator.
BACKGROUND
On-off waveforms with random transition times, i.e., random pulse trains, have found use in a variety of applications. One such class of applications is that of ultra-wide bandwidth radar and other radar-type applications. Random pulse trains can be used to generate electromagnetic impulses at random intervals, thus greatly reducing susceptibility of detection and/or jamming of the radar system by other electronic systems.
Commonly, pseudo-random pulse trains are generated using a linear feedback shift register (LFSR) as the pulse generator. While use of such pulse generators offers some protection from detection and jamming, the resulting pseudo-random pulse trains generally repeat at some regular interval. This periodicity of the pulse train increases the likelihood of detection and jamming of the radar system.
Attempts to improve the randomness of pulse generators have been described. See, e.g., U.S. Pat. No. 4,769,777 issued to Bittle et al. on Sep. 6, 1988 (Bittle et al.). Bittle et al. is fundamentally based on an LFSR, using a phase shift oscillator whose supply voltage is varied in time to interfere with the periodicity of the LFSR by altering the frequency of oscillation of the phase shift oscillator. Devices of Bittle et al. may also use variable thermal feedback to vary the frequency of the oscillator. However, for miniaturized applications, e.g., incorporating a relatively high rate random pulse generator on an integrated circuit device, thermal feedback may not be desirable or practicable for interfering with periodicity. Furthermore, as integrated circuits continue to operate on lower supply voltages, variation of supply voltage may also be impracticable as a means of interfering with periodicity.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternate methods of generating random pulse trains.
SUMMARY
The above-mentioned problems with random pulse generation and other problems are addressed by the present invention and which will be understood by reading and studying the following specification. Random pulse generators and systems are described herein using at least three oscillators, wherein the output signals of at least two of the oscillators are combined to disturb the output signal of a final oscillator. The final oscillator refers to the oscillator immediately preceding production of the random pulse train. For one configuration, combined output signals of at least two phase shift oscillators are used to modify the feedback signal of a final phase shift oscillator, thus disturbing the output signal of the final oscillator. For another configuration, the output signals of at least two phase shift oscillators are used to drive a subtractor whose output signal is combined with the output signal of a final phase shift oscillator to drive a subsequent subtractor, thus disturbing the output signal of the final oscillator. It is generally preferred that each oscillator have a different period. While pulse generators described herein are capable of exhibiting substantially random behavior and are referred to as random pulse generators, it is recognized that true random behavior is likely unattainable in electronic systems. However, systems designed in accordance with various embodiments of the invention are capable of sufficiently approximating random behavior to find use in applications such as those described above.
For one embodiment, the invention provides a random pulse generator. The random pulse generator includes a first oscillator having an output signal, a second oscillator having an output signal, and a third oscillator having an output signal. The output signal of the first oscillator and the output signal of the second oscillator are combined to disturb the output signal of the third oscillator.
For another embodiment, the invention provides a random pulse generator. The random pulse generator includes a first phase shift oscillator having an output signal and a feedback signal and comprising a first odd number of inverter segments, a second phase shift oscillator having an output signal and a feedback signal and comprising a second odd number of inverter segments, and a third phase shift oscillator having an output signal and a feedback signal and comprising a third odd number of inverter segments. The random pulse generator further includes a filter comprising a resistive component and having a first input of the output signal of the first phase shift oscillator, a second input of the output signal of the second phase shift oscillator, and a third input of the feedback signal of the third phase shift oscillator. The output signal of the first phase shift oscillator and the output signal of the second phase shift oscillator vary a resistance of the resistive component of the filter and the feedback signal of the third phase shift oscillator is coupled to the resistive component of the filter and is modified by varying the resistance of the resistive component of the filter.
For yet another embodiment, the invention provides a random pulse generator. The random pulse generator includes a first phase shift oscillator having an output signal and a feedback signal and comprising a first odd number of inverter segments, a second phase shift oscillator having an output signal and a feedback signal and comprising a second odd number of inverter segments, and a third phase shift oscillator having an output signal and a feedback signal and comprising a third odd number of inverter segments. The random pulse generator further includes a first subtractor coupled to the output signals of the first and second phase shift oscillators, wherein the first subtractor produces a first intermediate potential in response to the output signals of the first and second phase shift oscillators. The random pulse generator further includes a second subtractor coupled to the first intermediate potential and the output signal of the third phase shift oscillator, wherein the second subtractor produces a second intermediate potential in response to the first intermediate potential and the output signal of the third phase shift oscillator.
For a further embodiment, the invention provides a random pulse generator. The random pulse generator includes a plurality of first phase shift oscillators having a combined output signal, a second phase shift oscillator having an output signal and a feedback signal, and a third phase shift oscillator having an output signal and a feedback signal. The random pulse generator further includes a first subtractor coupled to the combined output signal of the plurality of first phase shift oscillators and the output signal of the second phase shift oscillator, wherein the first subtractor produces a first intermediate potential in response to the combined output signal of the plurality of first phase shift oscillators and the output signal of the second phase shift oscillator. The random pulse generator still further includes a second subtractor coupled to the first intermediate potential and the output signal of the third phase shift oscillator, wherein the second subtractor produces a second intermediate potential in response to the first intermediate potential and the output signal of the third phase shift oscillator.
For another embodiment, the invention provides a random pulse generating system. The random pulse generating system includes a random pulse generator having a random pulse train and at least one frequency divider each having an input signal and an output signal. The at least one frequency divider is coupled to the random pulse generator in series. The first frequency divider in t
Bauhahn Paul Eugene
Dvorak Mark Daniel
Bremer Dennis C.
Honeywell International , Inc.
Kinkead Arnold
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